1. Field of Invention
The present invention relates to an electron beam measurement method that measures the amount of electron beams radiated from a vacuum tube type of electron beam tube that is used in curing resists applied to semiconductor wafers, etc. and in drying ink applied to various types of printed material. The present invention also relates to an electron beam irradiation processing device that processes aforementioned processed material by irradiating it with electron beams.
2. Description of Related Art
The use of electron beam irradiation has been proposed to cure resists applied to semiconductor wafers as well as to dry or cure paint, ink, adhesive, protective resin, etc., applied to substrates.
In recent years, electron beam tubes provided with a window have been marketed. The structure of such electron beam tubes comprises a thermo-ionic unit and an electron beam acceleration unit mounted in a vacuum container provided with a window which is permeable to electron beams. The thermo-ionic electrons radiated from the thermo-ionic unit are accelerated by an electron beam acceleration unit and radiated.
Electron beams are radiated into the atmosphere from the window when such an electron beam tube is used. Conventional electron beam irradiation processing devices have depressurized the atmosphere in which the irradiated material is disposed. However, this is unnecessary when using aforementioned electron beam tube thereby eliminating the need for vacuum pumps and vacuum chambers for depressurization, and consequently, simplifying the structure of the electron beam irradiation processing device.
FIG. 7 is a diagram that shows the diagrammatic structure of a vertical type of electron beam tube provided with a window (hereinafter abbreviated EB tube) and its power source circuit.
EB tube 1 is provided with filament 1a and grid 16. High voltage of 30 to 70 kV, for example, is applied to filament 1a and grid 1b from direct current high-voltage power source 2 via terminal 1f. Furthermore, filament power source 3 is connected to filament 1a via terminal 1f. Filament 1a is heated by current that is provided from said filament power source 3 and thermo-ionic electrons are radiated. Electrons that are radiated are arranged in beam shape by an electric field that is created by grid 1b. In addition, grid power source 4 is connected to grid 1b via terminal 1f and electron emission from grid 1b can be controlled by controlling the voltage that is applied to grid 1b. 
The arranged electron beam (hereinafter termed xe2x80x9celectron beamxe2x80x9d) is output outside of EB tube 1 from window 1d that is set in flange 1c. The electron beams that are output from EB tube 1 are irradiated on processed material such as semiconductor wafers that are not illustrated or on various types of printed material to complete curing of resists or drying of ink, etc.
EB tube 1 has a sealed structure comprising quartz tube wall 1e, flange 1c and window 1d. The internal pressure is depressurized to 10xe2x88x924 to 10xe2x88x926 Pa (10xe2x88x926 to 10xe2x88x928 Torr) to ensure that the electron beams that were created are not attenuated.
Window 1d is a film of special material containing silicon of several xcexcm thickness (for example, 3 xcexcm) to ensure that the electron beams are not attenuated while passing through the window 1d. 
The electron beams that are created can be output outside of EB tube 1 more efficiently by enlarging the area of window 1d. However, the window is extremely thin (several xcexcm), as indicated above, and it must serve as a partition between the atmospheric pressure outside of EB tube 1 and the pressure (10xe2x88x924 to 10xe2x88x926 Pa) within EB tube 1. Accordingly, the area of one window cannot be too large because of the danger of breakage. Thus, a plurality of windows, each having a small area with a size of 1 to 2 mm per side, are aligned in the longitudinal direction of the filament so as to match the shape of the electron beams, as shown in FIG. 8.
A prescribed amount of electron beams must be irradiated onto processed material when processing the processed material (workpiece) using electron beams that are output from EB tube 1. If the processed material is not irradiated with the prescribed amount of electron beams and the amount of irradiation is inadequate or excessive, the processing of the processed material would fail.
The following two methods of outputting a fixed amount of electron beams have been available. Both effect controls so that a fixed amount of power is provided to EB tube 1.
[1] Method of control in which the tube current is detected and controlled so as to be constant. This is a method in which the tube current (the current flowing from direct current high-voltage power source 2 to EB tube 1 in FIG. 7, denoted by broken line in the diagram) is detected by current detection unit 5 and is controlled so as to be constant by controlling the current flowing through filament 1a, as shown in FIG. 7. This is control in which the power supplied to EB tube 1 is kept constant by holding the tube current constant so long as the voltage of direct current high-voltage power source 2 is constant. This method is usually used in X-ray tubes.
[2] Method in which the filament input power is held constant. This is a method in which the power input to filament 1a is controlled to be constant by controlling the current (and the voltage of filament 1a) that flows through filament 1a. The amount of thermo-ionic electrons that are emitted is controlled by controlling the power of filament 1a to be constant. More specifically, the tube current is controlled to be constant and the power supplied to EB tube 1 is held constant. Despite the control methods described above, the amount of electron beams output from EB tube 1 changes even if the tube current is controlled to be constant and a fixed level of power is supplied to EB tube 1, as shown in FIG. 7. The present inventors believe that the reasons for this are follows:
[1] Filament 1a and grid 1b within EB tube 1 are fixed within so that their positions would not change. However, the shapes of the filament 1a and of the nearby grid 1b change due to thermal expansion since the temperature of the heated filament reaches about 1900xc2x0 C. during thermo-ionic electron output.
[2] The shape and direction of the electron beams change due to the effects of the electrostatic charge that develops within the tube.
As mentioned above, window 1d that captures electron beams outside of EB tube 1 comprises a set of windows about 1 mm wide, each aligned in the longitudinal direction of the filament. Accordingly, electron beams are emitted beyond window 1d when the shape and direction of the generated electron beams change within EB tube 1 for aforementioned reasons [1] and [2], and those electron beams are no longer captured. As a result, the amount of output electron beams changes.
Accordingly, the present inventors believe that even if EB tube 1 could be controlled so that a constant power would be provided, the amount of electron beams output from EB tube 1 could not be held constant.
Therefore, there exists an unfulfilled need for an electron beam irradiation processing device and a method of control thereof that overcomes the above noted disadvantages.
The present inventors have found that the amount of electron beams could be controlled to be constant if the power supplied to EB tube 1 could be controlled in a manner that the amount of electron beams output from EB tube 1 were constant by measuring this electronic beam output from the EB tube 1. However, no method of accurately measuring the amount of electron beams output from EB tube 1 had been available. In particular, the atmospheric gases turn into plasma as a result of electron beam irradiation, resulting in secondary electron emission from the processed material, the workpiece stage upon which the processed material is set, and the walls of the processing chamber, etc. For such reasons, even if a sensor and the like were disposed near window 1d of EB tube 1 to detect the amount of electron beams, the amount of electron beams output from EB tube 1 could not be accurately and stably detected due to the effects of the floating charge attributable to aforementioned secondary electrons.
The present invention has been devised in light of the problems associated with conventional technology as discussed previously and above. In this regard, the first object of the present invention is to provide an electron beam measurement method capable of accurately measuring the amount of electron beams output from an electron beam tube to the processed material. The second object is to provide an electron beam irradiation processing device capable of controlling and holding constant, the amount of electron beams irradiated onto processed material by controlling and holding constant, the amount of electron beams output from an electron beam tube.
In accordance with the preferred embodiments of the present invention, the above objects are attained by:
(1) A current detection unit comprising a conductor or a semiconductor covered by an insulating film is disposed on the outside of the window of an electron beam tube and the amount of electron beams radiated from the electron beam tube is measured by measuring the current flowing through the current detection unit.
(2) A current detection unit comprising a conductor or a semiconductor covered by an insulating film, and a measurement unit for measuring the amount of electron beams comprising a current measurement unit that measures the current flowing through the current detection unit. These are disposed on the outside of the window of an electron beam tube to thereby allow measuring of the amount of electron beams output from the electron beam tube. The amount of electron beams irradiated onto the processed material can then be held constant by controlling the power source unit as a function of the current signal flowing through the current detection unit.
In accordance with one embodiment of the present invention, a current detection unit comprising a conductor or a semiconductor covered by an insulating film is disposed as mentioned above. The aforementioned insulating film forms an energy barrier and the amount of electron beams radiated from the electron beam tube can be measured by measuring the current following through the current detection unit. Accordingly, the generation of current through capture of the floating charge (i.e. the above noted secondary electron emission) by the aforementioned semiconductor or conductor can be prevented. For this reason, the current due only to electrons output that is generated from the electron beam tube can be detected, and electron beams output from the electron beam tube can be accurately measured.
Furthermore, the amount of electron beams output from an electron beam tube can be controlled without being affected by a floating charge. The amount of electron beams output from the electron beam tube can be controlled by applying aforementioned method of measuring the amount of electron beams to an electron beam irradiation processing device. Moreover, a fixed level of electron beams could be stably output even if the shape or direction of electron beams within the electron beam tube should change.
For this reason, processed material could be irradiated with a set, prescribed amount of electron beams, and processing failure due to insufficient or excessive irradiation could be prevented.